You are wrong my friend, Minato can be defeated there were many great ninja, legendary ninjas, Minato is one of them but not higher than them, we must understand all the legendary ninjas abilities then decide who's the stronger but we'll never find that out.
He was being sarcastic. lol.
I'll start by saying that Tsunade and A underestimated Naruto a lot so I won't count their judgement for being too accurate. Also we all know how everyone reacted when KinGin bros appeared on the battlefield, yet they went down fairly easy.
And tell me something: how is Oonoki planning to defeat Muu if he's always invisible? There must be quite a few weaknesses there and I am still assuming that we needs to be visible when attacking.
But I gotta say...I am curious know of who do you think would stand a good chance of defeating Muu
On detecting Invisible people/objects:
Generally, when something or someone is truly invisible (not visible and even erasing his own chakra), but you know it's there,
you look at the environment around it for changes it would affect to indirectly see it rather than try to look for it directly.
One trick that worked was sensor sand, but it could be a tree branch bending, leaves or sand blowing around and not through a pocket of air, etc.
Gaara would be great at assisting Onooki in my opinion due to him being in the desert and his control of sand. He could do sand sweeps and/or sand showers (just imagine the sand rain hitting the ground everywhere but one spot), and it would work very similar to sonar in a submarine movie/TV show (just an analogy, not science!), it would become immediately obvious to the viewer, Gaara, that there's a
hollow point that sand isn't passing through like it would the regular air.
That hollow point is where Muu is where Muu would be hiding. Thus, the desert isn't the best battlefield for him especially because Gaara is there.
That's just one way to detect him I can think up off the top of my head. Muu may make himself invisible and be able to erase his own chakra, but that doesn't stop him from affecting the environment around him, which is how I suppose the general strategy would go for following him. The one with Gaara is just a specific one.
This only resolves one problem, Muu still has plenty more. It's going to be interesting to see how dust vs. dust goes. Obviously Onooki has the advantage of being the next generation, so he's had much of his lifetime to work on enhancing his dust release bloodline expansion and not just developing it from scratch as Muu had to.
As well, Onooki et al. don't have the limitations of being Edo Tensei's, which until I see otherwise, seems to weaken each character that has ever been revived compared to when they lived (likely due to a combination of IWR jutsu and plot reasons).
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Also, Draegod why do you keep thinking everyone you make a thread about is "underrated" when they're immensely powerful and "almost unbeatable?" That's an oxymoron along with your poll for options of listing him in the top 5 and 10. Is it salesmanship or something? People are going to read the thread anyway, Muu is interesting.
This is a guy who can become invisible, erase his own chakra, is a sensor, dust release, weapons abilities, a former Kage, etc. Damn, what makes a normal rating for you?! What's a guy have to do? Last time it was Hashirama who had a petting zoo of Bijou, lol.
It's just odd to me, and
I'm not trying to be critical because it's kind of funny. I just don't think that lesser known characters are the same as underrated, but it's your thread, so continue this way, and I'll get to keep reading your threads, win-win.

Your style clearly works to draw people in, and you you seem well prepared when you open these threads. Thus, cheers I suppose. :hug: (I couldn't find a cheers smiley face, thought that this would do well enough).
Nice thread...
Peace